4.25.23 - Topic 4 - Homeostasis/Transport - Keystone Review

Which statement best describes a function of the proteins embedded in the plasma membrane of cells?

• They provide instructions for the processes in the cell.

• They selectively allow certain particles into and out of the cell.

• They attract charges in the cell’s environment to give the cell a net charge.

• They store the energy required by the rest of the membrane to perform its functions.

Answer explanation

Channel proteins and protein pumps regulate the movement of materials, such as gases and nutrients, across the plasma membrane.

The shivering mechanism in bumblebees often serves the same purpose as it does in mammals. During which condition will the action of shivering most help a bumblebee to maintain homeostasis?

• decrease in available oxygen

• low environmental temperature

• uncontrolled rise in core temperature

• depletion of oxygen in muscle tissues

Answer explanation

Shivering helps to return the body to an optimal temperature.

Tags

NGSS.HS-LS1-3

Carbon dioxide and oxygen are molecules that can move freely across a plasma membrane. What determines the direction that carbon dioxide and oxygen molecules move?

• Orientation of cholesterol in the plasma membrane.

• Concentration gradient across the plasma membrane.

• Configuration of phospholipids in the plasma membrane.

• Location of receptors on the surface of the plasma membrane.

Answer explanation

Diffusion is the movement of molecules from an area of high concentration to that of a lower concentration.

If the concentration of CO2 or O2 is too high on one side of the membrane, then the molecules would not freely be able to move from an area of high concentration to an area of low concentration

Which example is an activity that a fish most likely uses to maintain homeostasis within its body?

• Using camouflage to avoid predators.

• Feeding at night to regulate body temperature.

• Moving to deeper water to regulate metabolic wastes

• Exchanging gases through its gills to regulate oxygen levels.

Answer explanation

O2 is needed for cellular respiration to provide energy for the organism. At the gills, O2 and CO2 are exchanged. If CO2 is present, the amount of O2 will change to stay regulated.

Tags

NGSS.HS-LS1-3

Which of the following examples illustrates osmosis?

• Water leaves the tubules of the kidney in response to the hypertonic fluid

  surrounding the tubules.

• Digestive enzymes are excreted into the small intestine.

• White blood cells consume pathogens and cell debris at the site of an infection.

• Calcium is pumped inside a muscle cell after the muscle completes its

  contraction.

Answer explanation

Osmosis is the movement of water across a membrane due to differential solute

concentrations. Excretion of digestive enzymes is triggered by chemical changes in the

stomach. White blood cells are released in response to the presence of a pathogen.

Calcium is released when a nervous signal is sent to the muscle cells. Therefore, the

correct answer is choice A

In all reptiles, birds, and mammals, the processes of excretion, water and salt balance, and the regulation of pH in body fluids are controlled by the kidneys. This is an example of the organism maintaining

• reabsorption

• homeostasis

• insulation

• hibernation

Answer explanation

Choices A, C, and D are processes that occur as a result of organisms maintaining homeostasis. Choice B is the correct answer because that is the main process by which the others can occur.

Tags

NGSS.HS-LS1-3

Some animals can produce a potassium ion concentration inside their cells that is twenty times greater than that of their environment. This ion concentration gradient is maintained by the plasma membrane.

Part A: Identify the process in the cell membrane that produces this difference in concentration.

Part B: Explain the process that occurs as the cell produces the ion concentration gradient.

Part C: Compare the process of potassium ion transport to another mechanism that moves material across the plasma membrane.

Answer explanation

Part A: The process is active transport (needs energy).

Part B: There are specialized proteins in the cell membrane that act like “pumps with a toll”. These pumps use ATP (small packets of energy) to power their transport of Na+ out of a cell, and K+ into the cell. Because different numbers of sodium ions and potassium ions are pumped back and forth, it creates an electrical gradient where one side of the cell is more positive than the other side.

Pact C: Active transport is specific and also uses energy, which is the key distinction, as opposed to facilitated diffusion which is also specific to a molecule (or ion) but does not require energy. An example would be glucose is too big to pass through the cell membrane on its own, but can do so the with help of a specific protein.

Which cell process is best modeled by the diagram?

• osmosis

• exocytosis

• passive transport

• facilitated diffusion

Answer explanation

During exocytosis, a vacuole fuses with the cell membrane, releasing its contents outside of a cell.

The diagram shows the movement of ions against a concentration gradient to an area of higher concentration. Which molecule provides the energy needed for this movement to occur in a cell?

• ATP

• mRNA

• protein

• lipid

Answer explanation

ATP is an energy molecule that can be used to actively transport ions across a concentration gradient.

Tags

NGSS.HS-PS1-5

Which component of this membrane contains a hydrophobic region and acts as the primary barrier to most foreign substances?

• protein

• cholesterol

• carbohydrate chain

• phospholipid bilayer

Answer explanation

Each phospholipid of the bilayer consists of two main parts: a hydrophilic phosphate group and hydrophobic lipid tails. This structure allows the bilayer to be impermeable to most water-soluble (hydrophilic) molecules and ions.